Ch. 16 pt. 1&2

• Basic taste qualities

  • Salty
  • Sour
  • Sweet
  • Bitter
  • Umami (meaty, brothy or savory, associated with MSG)
• Components of the chemical senses

  • Taste (molecules enter mouth and stimulate receptors on tongue)
  • Olfaction (air-borne molecules enter nose and stimulate receptors in olfactory mucosa)
  • Flavor (impression from combination of taste and olfaction)
• Neurogenesis in chemical senses


  • Constant renewal of receptors unique to taste and smell
  • Cycle of birth, development, and death over 5–7 weeks for olfactory receptors and 1–2 weeks for taste receptors
• Chemical senses as "gatekeepers"

  (1) Identify things body needs for survival and should be consumed

  (2) Detect things that would be bad for body and should be rejected
• Things bad for us

  Often taste or smell unpleasant
• Things good for us

  Generally taste or smell good
• Smelling an odor

  Can trigger memories and emotional reactions
• 4 taste qualities and associated substances

  • Sodium Chloride (salty)
  • Hydrochloric Acid (sour)
  • Sucrose (sweet)
  • Quinine (bitter)
• Potassium Chloride (KCl)


  Has substantial salty and bitter components
• Sodium Nitrate (NaNO3)


  Results in a taste consisting of a combination of salty, sour, and bitter
• Sweetness


  Usually associated with substances that have nutritive value
• Bitter


  Usually associated with substances that are potentially harmful
• Salty taste


  Indicates the presence of sodium
• There is not a perfect connection between tastes and function of substances
• Types of papillae on the tongue

  • Filiform: mechanical function (shaped like cones, located over entire surface)
  • Fungiform (shaped like mushrooms, found on sides and tip)
  • Foliate: don't use them as adults, but as babies to detect milk (series of folds on back and sides)
  • Circumvilliate (shaped like flat mounds in a trench located at back)
• Pathways for signals from taste cells

  • Chorda tympani nerve (from front and sides of tongue)
  • Glossopharyngeal nerve (from back of tongue)
  • Vagus nerve (from mouth and throat)
  • Superficial petronasal nerve (from soft palate)
• Brain areas involved in taste processing

  • Nucleus of the solitary tract (in spinal cord)
  • Thalamus
  • Insula
  • Frontal operculum cortex
  • Orbital frontal cortex
• Population Coding: we don't perceive taste due to the activation of only 1 receptor but rather triggers many fibers

  • activity in many different neurons, respond to different features, all put together to create representation
• Erickson's experiment demonstrated population coding in rats
• Erickson's experiment on similarity judgments in humans supported population coding
• Specificity coding


  Analyzing text-based data to gauge the level of detail in qualitative research
• Mueller et al's experiment successfully created mice with a human receptor that responds to PTC
• Recordings from neurons show some are specialized to respond to specific stimuli, while others respond to multiple stimuli</b>
• Applying amiloride to the tongue blocks sodium flow and decreases responding of neurons that respond to salt, but not those that respond to salty and bitter
• Individual differences in taste

  • Tasters, nontasters, and supertasters
  • Presence of specialized receptors
• Tasters: have more taste buds than nontasters, and have specialized receptors for compounds like PTC and PROP
• Supertasters: appear more sensitive to bitter substances than tasters
• Humans are microsmatic (less keen sense of smell) compared to macrosmatic animals like rats and dogs
• Measuring detection threshold


  Yes/No Procedure (can result in bias)

  Forced-Choice (indicates which smells strongest)
• Rats are 8 to 50 times more sensitive to odors than humans, and dogs are 300 to 10,000 times more sensitive, due to having more receptors
• Humans can discriminate more than one trillion different odors, but only successfully identify odors about half the time
• It is difficult to map perceptual experience of odors onto physical attributes of odorants
• Links have been found between the structure of molecules, olfactory quality, and patterns of activation in the olfactory system
• Olfactory mucosa: located at top of nasal cavity, where odorants contact olfactory receptor neurons
• Humans have about 350 types of olfactory receptors, each with a 7-transmembrane protein
• Two stages of olfactory processing

  • Stage 1 (olfactory mucosa and bulb): Analyzing chemical components and transforming into neural activity

  Stage 2 (olfactory cortex and beyond): Synthesizing odor perception
• Brain areas involved in olfactory processing

  • Primary olfactory (piriform) cortex and amygdala

  Secondary olfactory (orbitofrontal) cortex
• Amygdala plays a role in emotional reactions to odors
• Rennaker's experiment showed isoamyl acetate causes widespread activation in the piriform cortex
• Wilson's experiment showed the piriform cortex could discriminate between a mixture and a compound odorant with enough exposure